To keep the launch price under £400, Sinclair left out many items that most owners would consider essential, such as indicators, mirrors and the High-Vis Mast, and sold them as accessories. The C5 Accessories catalogue (9 pp.) came in every owner's pack. Accessories were ordered direct from Sinclair Vehicles Ltd (FREEPOST, Camberley), by post or by phone with Access, Barclaycard or Trustcard. Each one carried a one-year guarantee and a 7-day money-back offer.

Post and packing was £2.45 for orders under £25, £2.95 for £25–£50, and free over £50. Mainland UK only.

Later stockists (Turbinecharm and ESG, Liverpool, 1989–91) sold the same extras at £7.95–£34.95, the charger at £39.23, a battery master security switch at £37.95 (C5674 395), the external battery fitting kit at £27.83 and a battery at £72.

• Kit contents: front repeater assemblies ×2, rear assemblies ×2, flasher, switch, 4-way and 3-way terminal blocks, 15 cable clips, 250 mm black/white wire, hole cutter, template, lockplates and spring clips.
• Wiring: most of it is already in the C5. The connecting wires are stowed as a folded loop inside the black tubular trunking on the seat back, and the repeater wires connect to the existing 9-way bundle to the pod using the 3-way block.
  • Colours: Violet/White, Red/White, Blue/White, Black/White.
  • Alternative harness: if the wiring differs, look for a cluster of 6 connectors under the tunnel near the rear brake arm. In that case cut back the trunking about 40 mm and fit the 4-way block, cutting and joining the Blue/White, Red/White and Violet/White loops.
• Front repeaters: use the template to drill three 2 mm holes, then open out the centre hole to 16 mm with the supplied cutter. Fit with the lens “weep” hole at the bottom.
• Switch: mounts on a plate on the extreme right-hand edge of the seat, with two self-tapping screws in 2 mm pilot holes. Wires go through a 10 mm hole in the bulkhead.
• Rear indicators: drill two 2 mm pilot holes per the template, open out to 10 mm, then fit with a foam gasket and spring clip.
• Bulbs: front repeaters 12 V 5 W wedge; rear 12 V 10 W festoon.
• Cable clips: these are self-adhesive. Clean the surface with warm water and detergent first, then press firmly for a few seconds.

• Kit contents: horn with leads, 5 cable clips, brake clamp and switch with leads, bolt, nut and washer, 4-way terminal block, 250 mm black/white wire.
• Switch: remove the steering-bar cover, peel back the right-hand grip, and replace the brake-lever bracket clamp with the new clamp and switch assembly. Plug its two wires into the empty connectors on top of the steering stem, matching colours.
• Horn: bolt it to the rear wall of the left footwell through a 5.5 mm hole, using the template.

• Kit contents: 2 mounting poles, reflector moulding, red and white reflective decals, 2 small plugs, 2 large plugs, 2 drive rivets.
• Fitting:
  1. Apply the decals: red to the rear, white to the front.
  2. Fit drive rivets into the pole ends.
  3. Remove the plugs from the grommets on top of the seat back and push the poles in until they locate in the cups under the top of the seat back.
  4. Smear petroleum jelly inside the top of the poles, push in the small ball plugs, and press the reflector moulding on.
  5. Remove the rear lamp and press the large plugs into the cups at the top of the rear location frame.
• Removal: take off the reflector moulding without distorting the lugs, then pull the poles up. You need to do this to fit the tonneau.
• Which? reported all the masts on its test vehicles snapping. The AA, Which? and the Dutch authorities all said the mast should have been standard equipment.

• Kit contents: mirror (L or R), spacer, fracture plate, 2 screws, 2 lockwashers, 2 washers, 2 square nuts.
• Fitting: use the spacer as a template to drill two 3 mm horizontal holes through the body flange. Fit the fracture plate and spacer, then the mirror case, with the square nuts captured inside the case flange. Don't overtighten.
• The fracture plate is deliberately designed to break in an impact.

• Fitting: the retaining plate is fitted with plastic rivets into existing holes in the right-hand footwell. The two-part strap anchorages need 3 mm holes drilled using the template, with large reinforcing washers on the outside.
• Two ways to use it (Sinclair “Using a Second Battery” sheet, part no. 100959/3/85):
  1. As a spare. Swap it into the left footwell when the first battery is flat. Never drive on the right-hand battery alone. Only the left-hand battery is monitored by the protection circuit.
  2. In parallel, using the second-battery connection kit and a second (right-hand) master security switch.
     • Both batteries must be at the same state of charge.
     • Switch the left-hand switch to D first, then the right. Otherwise the battery-sensing circuit won't work properly.
     • Remove the right-hand key before driving.
     • Both cut-out buttons must be pressed to isolate the motor.
• Safety: with the left battery switched on, the terminals of a parked right-hand switch are live. Always secure it in its park bracket.
• Charging: use one charger per battery. Don't charge both from one charger.
• Range is up to about 40 miles with two batteries (Sinclair's claim). Wiring them in parallel gives more than using them one after the other; see Specifications.

• Squire cablelocks No. 672 (6 ft, multi-warded, about £3.99) and No. 536 (6 ft, pin tumbler, about £5.45). Sinclair recommended these in the leaflet Security for Your Sinclair C5. A proprietary lock was a condition of the Prudential C5 insurance scheme.
• Prudential Sinclair C5 insurance scheme, with its own leaflet in the pack.
• C5 Registration Card and personalised number plate, free on returning the application form. Museum Wales holds an example (1996.111/24–25).
• The RoSPA Guide to Safe Driving in the Sinclair C5, a booklet in every owner's pack.
• C5 Hotline: 0276 685551. Owners were told to call this for the first 3 months instead of the service network.

• C5 Accessories catalogue (Sinclair Vehicles, 1985, ref. SAC 501). Scan on c5owners.com; Museum Wales 1996.111/4.
• Sinclair fitting instructions for direction indicators, horn, High-Vis Mast, rear-view mirror and spare battery kit, plus “Using a Second Battery”. Scans on c5owners.com; also reproduced in The Unofficial Sinclair C5 Service Manual, pp. 30–45.
• Turbinecharm Ltd (Dec 1989) and Ellar Surplus Goods (Dec 1991) parts and price lists, c5owners.com.
• “Security for Your Sinclair C5” leaflet; “Owners Pack – Read This First” letter from B.G. Wills; “C5 Hotline Tips”.